1. Field of the Invention
The present invention generally relates to lens modules and, more particularly, to a lens module for an optical device such as a microscope, a camera module, a digital camera module used in a portable electronic device, or such like.
2. Description of Related Art
With the ongoing development of microcircuitry and multimedia technologies, digital cameras are now in widespread use. High-end portable electronic devices, such as mobile phones and personal digital assistants (PDAs), are being developed to be increasingly multi-functional. Many of these portable electronic devices are now equipped with a digital camera module. These electronic devices enable consumers to enjoy capturing digital pictures anytime and anywhere. At the same time, the demand for digital picture quality has become greater and greater.
In a digital camera, a lens module is very important to the quality of the pictures captured by the digital camera. Referring to FIG. 5, a typical lens module 100 includes a barrel 11, a lens 12 and an image sensing module 13. The barrel 11 is a hollow cylinder and includes an inner surface 110, a screening end 111 and a mounting end 112 positioned opposite to the screening end 111. An aperture 113 for receiving optical image signals is defined in a central portion of the screening end 111. The aperture 113 reduces in diameter from the screening end 111 to the mounting end 112, a cone-shaped surface 114 is thus formed on the screening end of the barrel 11 and unwanted light is thus prevented from entering the barrel 11.
The lens 12 is mounted in the barrel 11. The image sensing module 13 includes an image sensor 131, a top board 132 and a base board 133. The image sensor 131 is mounted on the base board 133. The top board 132 is made of transparent material such as glass or plastic. Periphery of the top board 132 is mounted on the base board 133, thus packaging the image sensor 131 between the top board 132 and the base board 133.
In assembly, the image sensing module 13 is mounted on the mounting end 112 of the barrel 11, the image sensor 131 is located in an light-path of the lens 12, and the top board 132 is disposed between the lens 12 and the image sensor 131. In use, light enters the barrel 11 from the aperture 113 and is focused by the lens 12 to form an object image on the image sensor 131.
However, when using the lens module 100, some stray light is likely to enter the barrel 11 and interferes with the object image formed on the image sensor 131. For example, some stray light A that is transmitted near the cone-shaped surface 114 and is approximately parallel to the cone-shaped surface 114 may enter the barrel 11 via the aperture 113. The light A reaches the inner surface 110 and is reflected to the image sensor 131 by the inner surface 110. Some stray light B and C that is transmitted to an area near a center of the aperture 113 may enter the barrel 11. Wherein the light B is reflected to the image sensor 131 by the inner surface 110. The light C is reflected to the inner surface 110 by the base board 133, and then reflected to a surface of the lens 12 by the inner surface 110, and is finally reflected to the image sensor 131 by the surface of the lens 12. The light A, B and C can interfere with the object image formed on the image sensor 131.
Therefore, an improved lens module is desired in order to overcome the above-described shortcomings.